Slipsheet retainer for bulk depalletizer/palletizer

ABSTRACT

An apparatus that is one part of a conveying system for transferring objects, such as bottles, removes layers of the objects from a pallet on which the layers have been stacked or, in reverse operation, arranges the objects in layers stacked on one another on a pallet. The apparatus may be employed to depalletize objects or to palletize objects, where in the depalletizing mode of operation the apparatus has a slipsheet retainer that holds a slipsheet below a layer of objects being depalletized from the stacked layers of objects on the pallet and prevents the slipsheet from moving with the layer of objects as the layer of objects is depalletized.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The present invention pertains to an apparatus that is one part of aconveying system for transferring objects, such as bottles, where theapparatus removes layers of the objects from a pallet or, in reverseoperation, arranges the objects in layers on a pallet. In particular,the present invention pertains to an apparatus that may be employed todepalletize objects or to palletize objects, where in the depalletizingmode of operation the apparatus has a slipsheet retainer that holds aslipsheet below a layer of objects being depalletized from the stackedlayers of objects and prevents the slipsheet from moving with the layerof objects as the layer of objects is depalletized.

(2) Description of the Related Art

Many containers such as bottles, cans, jars, jugs, etc. are packaged onpallets for transportation from a manufacturer to a user of thecontainer or object. The pallet loads often include layers of theobjects, each separated by a paperboard slipsheet, stacked on top of apallet constructed of wood. The layers of objects and the slipsheets onwhich the layers rest are secured on the top surface of the pallet bybanding, plastic sheet wrap or by other equivalent methods. The palletloads facilitate the transportation of a significant number of theobjects on each pallet load from the manufacture of the objects, throughdistribution and ultimately to the end user of the objects.

Upon receipt of a pallet load of objects the user of the objects removesthe banding or sheet wrap that secured the objects to the top surface ofthe pallet and then must unload the pallet by removing the topmost layerof objects on the pallet load, removing the slipsheet that supported thetopmost layer, then removing the next lower layer of objects from thepallet load and its slipsheet until the pallet is completely unloaded.In many conveyor systems in which objects are unloaded from pallet loadsand/or are loaded onto pallets, the faster the system can operate tounload and/or load pallets the more cost efficient is its operation.With manual unloading and loading of pallets being long recognized asslow and expensive, a number of different types of machines have beendeveloped over time that quickly perform the function of unloadingand/or loading pallets. These machines are referred to as depalletizersand/or palletizers in the conveying industry. Examples of these types ofmachines are described in U.S. Pat. Nos. 2,774,489, 3,780,884;3,844,422; 3,954,190; 3,974,922; 4,058,225; 4,197,046; 4,214,848, and4,557,656 the disclosures of all of which are incorporated herein byreference.

FIG. 1 is a schematic representation depicting a depalletizer,palletizer apparatus that comprises many features found in other priorart apparatus. The machine shown in FIG. 1 includes an object infeedsection A, an elevator section B, and an object outfeed section C. Asstated earlier, machines of this type are known in the prior art andvarious examples of these machines are disclosed in the above-listedpatents. In order to simplify the explanation of the construction andoperation of these types of machines the drawing of the machine in FIG.1 has been simplified, deleting many of the intricate component parts ofthe machine, examples of which are disclosed in the above-listedpatents, that enable the machine to function in the manner to bedescribed. The machine will be described as depalletizing andpalletizing objects, in this case plastic blow-molded bottles as shownin FIG. 1. It should be understood that "objects" is intended to meanany of the various different types of objects that may be transported inpallet loads and is not intended that the interpretation be limited toplastic bottles.

The sections of the machine shown in FIG. 1 are all supported by aframework 10. At the object infeed section A, the framework supports theend of a conveyor depicted as a belt and pulley conveyor 12. However,any other type of known conveyor may be employed to transport pallets ofobjects to the machine infeed section A. As shown in FIG. 1, the infeedconveyor 12 has transported a pallet load into the object infeed sectionA. The pallet load is comprised of several layers of objects 14, in thisexample plastic bottles, that are each separated from each other by apaperboard slipsheet 16 positioned under each layer of objects 14. Thelayers of objects 14 and the slipsheets 16 are all supported on a pallet18, for example a wooden pallet although pallets are constructed ofother types of materials. As shown in FIG. 1, the banding or plasticsheetwrap that usually secures the layers of objects 14 and slipsheets16 to the top surface of the pallet 18 has been removed. With the palletload of objects 14 positioned by the infeed conveyor 12 in the objectinfeed section A, the control system of the machine has preciselypositioned the pallet load relative to the sections of the machine topermit the quick depalletizing of each layer of objects in the palletload. The direction of movement of the infeed conveyor 12 may bereversed for operation in a palletizing mode.

Shown at the top of the object infeed section A is a sweeper mechanism22. The sweeper mechanism 22 has a generally rectangular base 24 at itstop that is supported in the machine to move horizontally across thelength of the machine between the object infeed section A and the objectoutfeed section C, and also to move vertically in the elevator section Bas will be explained. Suspended from four edges of the base 24 are fourside plates 26, only three of which are visible in FIG. 1, that aresuspended from the four edges of the base 24. A pivot rod supports eachof the side plates 26 from each edge of the base 24 for relativepivoting movement of the side plates 26 to the base 24 as represented bythe arrows in FIG. 1. The pivoting movement of the side plates 26 iscontrolled by pneumatic actuators that can be controlled to pivot theside plates 26 upwardly to positions that are substantially horizontaland parallel with the base 24.

A gripper mechanism 28 is also supported by the frame in the objectinfeed section A of the machine. The gripper mechanism 28 is supportedby the frame for vertical movement of the mechanism across the entirevertical height of the object infeed section A. The gripper mechanism 28comprises a pair of jaws 32 that are controlled to close and grip theback edge of a slipsheet 16 in depalletizing operation of the machine aswill be explained.

An elevator mechanism 34 is supported in the elevator section B of themachine. The elevator mechanism 34 is supported for vertical movementacross the vertical height of the elevator section B. The elevatormechanism 34 has a smooth, flat top sliding surface 36 that iscontrolled by the control system of the machine to be selectivelypositioned by the elevator mechanism adjacent the tiers of slipsheets 16and the top surface of the outfeed conveyor to be described. In someprior art machines of this type the elevator mechanism 34, the sweepermechanism 22 and the gripper mechanism 28 are all part of the same unitand move together vertically. However, these mechanisms can also be madeto move independently of each other.

An end of an outfeed conveyor 38 is supported in the machine frame inthe object outfeed section C. The outfeed conveyor 38 is depicted as abelt and pulley conveyor but may be any other type of conveyor. As withthe infeed conveyor 12, the conveying direction of the outfeed conveyor38 may be reversed in order to employ the machine in both adepalletizing mode and a palletizing mode.

The operation of the representative depiction of the prior artdepalletizer/palletizer shown in FIG. 1 is similar to the operation ofmost prior art palletizer/depalletizers. In the depalletizing mode ofoperation, a pallet load consisting of a pallet 18 having layers ofobjects 14 arranged thereon with each layer separated by a slipsheet 16is transported by the infeed conveyor 12 in a downstream direction untilthe pallet load is in its proper position in the object infeed section Aas shown in FIG. 1. The positioning of the pallet load in the objectinfeed section is controlled by sensors so that the layers of objects 14and their slipsheets 16 are in desired positions relative to theelevator section B and the gripper mechanism 28. If the sweepermechanism 22 is positioned in the object infeed section A as the palletload is conveyed to this section it must be moved completely to the topof the infeed section A in the position shown in FIG. 1 and at least theone side plate 26 shown at the right of the sweeper mechanism 22 in FIG.1 must be raised to provide clearance inside the remaining threedepending side plates 26 of the sweeper mechanism to receive the topmostlayer 42 of objects on the pallet load. If the sweeper mechanism 22 ispositioned in the elevator section B or the object outfeed section C, itis first raised to its topmost position and then the same side plate 26facing the pallet load is raised. The sweeper mechanism is then movedhorizontally over the topmost layer 42 of objects to its position shownin FIG. 1. With the sweeper mechanism 22 positioned over the topmostlayer 42 of objects, the side plates 26 are moved to their downwardlydepending position where their interior, mutually opposed surfaces comeinto contact around the grouping of objects 14 in the topmost layer 42.Also, prior to insertion of the pallet load in the object infeed sectionA by the infeed conveyor 12, the gripper mechanism 28 must be raised tothe top of the object infeed section A where it will be high enough toclear the topmost layer of objects 42 of the pallet load as they aremoved into the object infeed section.

Next, the elevator mechanism 34 is raised so that the sliding surface 36is adjacent the topmost slipsheet 44 as shown in FIG. 1. With thesliding surface 36 of the elevator mechanism 34 adjacent the topmostslipsheet layer 44, the gripper mechanism 24 is lowered from itsposition at the top of the object infeed section until it also isadjacent the topmost slipsheet layer 44 on the opposite side of theelevator mechanism sliding surface 36 as shown in FIG. 1. The jaws 32 ofthe gripper mechanism 28 are then operated to clamp along the rearwardedge of the topmost slipsheet layer 44 as shown in FIG. 1.

With the jaws 32 of the gripper mechanism 28 holding the rearward end ofthe topmost slipsheet layer 44, the sweeper mechanism 22, with its sideplates 26 all depending downwardly, next moves to the left as shown inFIG. 1. This motion of the sweeper mechanism 22 slides all of theobjects in the topmost layer 42 to the left sweeping the objects off ofthe topmost slipsheet 44 held by the gripper mechanism 28 and onto thetop sliding surface 36 of the elevator mechanism 34. This horizontalmovement of the sweeper mechanism 22 is controlled to position all ofthe objects in the topmost layer 42 on the elevator mechanism slidingsurface 36, and then the horizontal movement of the sweeper mechanism 22is stopped by the control system of the machine.

With the topmost layer of objects 42 positioned on the sliding surface36 of the elevator mechanism 34, the gripper mechanism 28 is disengagedand the elevator mechanism then moves vertically downward. As theelevator mechanism moves vertically downward the sweeper mechanism 22 iscontrolled to travel with the elevator thereby holding the topmost layerof objects 42 in a group on the sliding surface 36 of the elevatormechanism. The downward movement of both the elevator mechanism and thesweeper mechanism continues until the sliding surface 36 of the elevatormechanism is positioned adjacent the outfeed conveyor 38.

With the sliding surface 36 of the elevator mechanism positionedadjacent the outfeed conveyor 38, the sweeper mechanism 22 then moveshorizontally to the left as shown in FIG. 1, sweeping the topmost layerof objects 42 onto the outfeed conveyor 38. At this point in itsoperation, the outfeed conveyor 38 is not activated or operates for ashort time as the sweeper mechanism 22 sweeps the topmost layer ofobjects 42 onto the stationary outfeed conveyor 38. The sweepermechanism is controlled to position all of the objects of the topmostlayer on the outfeed conveyor, and then to raise vertically to the topof the object outfeed section C. The sweeper mechanism 22 then moveshorizontally to the right as viewed in FIG. 1 across the elevatorsection B to the top of the object infeed section A. Simultaneously withthis movement of the sweeper mechanism 22, the elevator mechanism 34raises in the elevator section B until the sliding surface 36 of themechanism is positioned adjacent the next lower slipsheet 46 of thepallet load. With the elevator mechanism in place adjacent the nextlower slipsheet 46, the sweeper mechanism 22 moves downwardly in theobject infeed section A to a position where the base 24 of the mechanismis just above the next lower layer of objects 48 and its side plates 26surround all of the objects in this layer. The gripper mechanism 28 alsomoves downward and grips the next slipsheet 46. The sweeper mechanism 22then moves to the left in the same manner as described earlier to sweepoff the next lower layer of objects 48 together with the slipsheet 44 ontop of the layer of objects onto the sliding surface 36 of the elevatormechanism. The process continues as described earlier until all of thelayers of objects are swept off the pallet 18 and onto the outfeedconveyor 38. The slipsheets 16 left on top of the layer of objects thathave been depalletized are later removed downstream in the conveyorsystem.

Alternatively, in the operation of prior art machines of this type, oncethe sweeper mechanism 22 has swept the layer of objects from the slidingsurface of the elevator mechanism 34 onto the outfeed conveyor 38, boththe elevator mechanism and sweep mechanism together move verticallyupwardly in the elevator section with the elevator mechanism 34 beingcontrolled to stop adjacent the next lower slipsheet 46 and the sweepermechanism 22 moving to the top of the elevator section. The sweepermechanism 22 then moves horizontally from the elevator section B to theobject infeed section A and then vertically downward over the next lowerlayer of objects 38 to be swept out of the object infeed section off ofthe pallet load.

Also in the operation of prior art machines of this type, depending onthe size of the objects being swept from the pallet load, it may benecessary for the control system of the machine to raise the side plates26 of the sweeper mechanism 24 as it moves horizontally over the palletload after the topmost layer of objects 42 has been swept from thepallet load.

It can be seen that when the last layer of objects 52 has been swept offthe last slipsheet 54 and onto the elevator sliding surface 36, theobject infeed section A of the machine is empty except for the presenceof the pallet 18. In prior art machines of this type, there are variousdifferent types of mechanism that are employed to remove the pallet 18,for example a separate conveying system for the emptied pallet thatwould extend transverse to the flow path from the infeed conveyor 12through the machine to the outfeed conveyor 38. With the pallet removedfrom the object infeed section A, this section of the machine isprepared to receive the next pallet load of objects, even while thesweeper mechanisms 22 is sweeping the last layer of objects 52 acrossthe elevator sliding surface 36 onto the outfeed conveyor 38. When thelast layer of objects 52 is removed from the pallet the grippermechanism 24, holding the last slipsheet 54 on the top surface of thepallet 18, releases the slipsheet so that both the pallet and slipsheetmay be removed from the object infeed section A. However, at this timethe gripper mechanism 28 is toward the bottom of the object infeedsection A just above the infeed conveyor 12. The infeed conveyor 12 mustthen wait until the gripper mechanism 28 is raised up to the top of theobject infeed section A so that the next pallet load of objects can bemoved into the object infeed section on the infeed conveyor 12. Thismovement of the gripper mechanism 28 out of the path of pallet loads onthe infeed conveyor 12 delays the time in which the next pallet load canbe moved into the object infeed section and the depalletizing of thispallet load can commence. With machines of this type being more costefficient by depalletizing layers of objects from a pallet load asquickly as possible, any delay in the depalletizing operation such asthat caused by the repositioning of the gripper mechanism 28 back to thetop of the object infeed section A lowers output efficiency and therebyincreases the cost of operating the conveyor system.

SUMMARY OF THE INVENTION

The present invention provides an improvement to adepalletizer/palletizer machine such as that shown in FIG. 1 byreplacing the slipsheet gripper mechanism 28 of the prior art machinewith a slipsheet retainer that, at all times of its operation, is notpositioned in the path of pallet loads transferred by the infeedconveyor 12 into the object infeed section A of the machine.Furthermore, the slipsheet retainer of the invention may be employed ona machine that is strictly a depalletizer, or may be employed on amachine that operates as both a depalletizer and a palletizer.Furthermore, the slipsheet retainer of the invention includesimprovements to the sweeper mechanism side plates 26 that enhance theability of the slipsheet retainer to hold back the slipsheet 16 belowthe layer of objects being swept from the pallet load by the sweepmechanism even when edges and corners of the slipsheet have been bentand when one or more objects around the peripheries of the layers ofobjects in the pallet load have fallen from their layer. The slipsheetretainer of the invention also comprises a mechanism for engagingagainst the next lower object layer as the topmost layer is being sweptfrom the pallet load to hold the objects in the next lower layer as thelayer above them is being swept off the pallet load and onto theelevator mechanism sliding surface.

The improvement of the invention provide a series of pneumaticallyactuated fingers on the leading edge of the elevator mechanism slidingsurface closest to the pallet load. The fingers are positioned beneaththe sliding surface of the elevator mechanism and are controlled toraise through slots to positions just above the sliding surface of themechanism. With the fingers raised, they are in position to engage theleading edge of the slipsheet of the topmost layer of objects in thepallet load as that layer of objects is swept by the sweeper mechanismonto the elevator sliding surface. The pneumatic force holding thefingers in their raised position is adjustable to be sufficient torestrain the slipsheet from moving with the topmost layer of objects asthe topmost layer of objects slide across the slipsheet by the motion ofthe sweeper mechanism, but is not a sufficient force to obstruct thesliding movement of the layer of objects. As a result, as each object inthe group of the top layer of objects passes into engagement with thepneumatically raised fingers the objects cause the fingers to pivotrearwardly against their pneumatic pressure permitting the objects topass causing some fingers to deflect according to the contour of theobjects as the objects are swept forward over the deflected fingers.Once the object has passed over the fingers, the fingers presseddownwardly by the passage of the object return to their raised positionsunder the force of the pneumatic pressure. With the staggeredarrangement of objects in each layer on the pallet load there are alwaysa number of pneumatically raised fingers in engagement with the edge ofthe slipsheet retaining the slipsheet from moving with the layer ofobjects being swept by the sweeper mechanism.

Each of the fingers is dimensioned to project a sufficient distanceabove the elevator mechanism sliding surface to engage the edge of theslipsheet even if the edge is bent upwardly. Where the slipsheetretainer encounters an edge of a slipsheet that has a significant bend,the side plate of the sweeper mechanism closest to the elevatormechanism also has a plurality of pneumatically actuated arms thatextend downwardly from the side plate and press down on the top of theupper most slipsheet at its edge closest to the elevator mechanism. Thisinsures that the leading edge of the slipsheet is positioned adjacentthe raised fingers of the slipsheet retainer so that the fingers willengage the edge and prevent the slipsheet from sliding onto the elevatormechanism as the sweeper mechanism slides the topmost layer of objectsonto the sliding surface of the elevator mechanism.

Together, the plurality of pneumatic fingers on the sliding surface ofthe elevator mechanism and the plurality of pneumatic arms on thesweeper mechanism side plate retain the slipsheet below the topmostlayer of objects on the pallet load as that layer of objects is sweptoff of the slipsheet and onto the sliding surface of the elevatormechanism. In palletizing operations, the plurality of fingers of theslipsheet retainer are lowered below the elevator mechanism slidingsurface and held in these retracted positions.

The slipsheet retainer of the invention also includes a pneumaticallyactuated hold back bar that is positioned just below the retainerfingers and extends outwardly from the elevator mechanism to engage thenext lower layer of objects on the pallet load. The hold back barensures that objects in the next lower layer of objects do not fall overas the sweeper mechanism sweeps the topmost layer of objects from theslipsheet above the next lower layer of objects.

Still further, the slipsheet retainer of the invention includes amechanism that moves the sliding surface of the elevator mechanismhorizontally relative to the elevator mechanism. For depalletizingoperations, this mechanism moves the sliding surface about four inchestoward the pallet load thereby minimizing the distance between theslipsheet and the elevator mechanism sliding surface across which thetopmost layer of objects must be swept by the sweeper mechanism. Forpalletizing operations, the sliding surface of the elevator mechanism iscontrolled to extend six inches from the elevator mechanism spanning thegap between the elevator mechanism and overlapping the slipsheet on thepallet in the object infeed section onto which layers of objects are tobe loaded.

The above-described slipsheet retainer provides an effective mechanismto restrain the movement of the topmost slipsheet of a pallet load asthe topmost layer of objects on the pallet load is depalletized withoutcausing a delay to the movement of the next pallet load of objects to bedepalletized. It also provides a mechanism that effectively restrainsslipsheets as layers of objects are unloaded from a pallet load evenwhere the slipsheet has been damaged and the edges of the slipsheet havebeen significantly bent upwardly or downwardly. The slipsheet retainerof the invention may be used in a machine that both depalletizes andpalletizes, or can be easily adapted to perform only the depalletizingoperation.

BRIEF DESCRIPTION OF THE DRAWINGS

Further objects and features of the invention are revealed in thefollowing detailed description of the preferred embodiments of theinvention and in the drawing figures wherein:

FIG. 1 is a schematic representation of a prior artdepalletizing/palletizing machine;

FIG. 2 is a half-section view of a platform of the retaining mechanismof the invention mounted on portions of an elevator;

FIG. 3 is a left-side elevation view of the platform of FIG. 2;

FIG. 4 is a half-section front elevation view of the platform of FIG. 2;

FIG. 5 is a half-section top plan view of a sliding plate that coversthe platform of FIG. 2;

FIG. 6 is a partial elevation view of a sweeper mechanism side plate;

FIG. 7 is a side elevation view, in section, of the side plate of FIG. 6showing an arm extended;

FIG. 8 is a side elevation view, in section, of the side plate of FIG. 6showing an arm retracted.

FIG. 9 is a side elevation view of the platform and slide plate alongline A--A of FIG. 2 showing a retaining finger retracted;

FIG. 10 is a side elevation view similar to that of FIG. 9 showing theretaining finger extended;

FIG. 11 is a side elevation view of the platform and slide plate alongline B--B of FIG. 2 showing a hold back bar extended;

FIG. 12 is a side elevation view similar to that of FIG. 11 showing thehold back bar retracted;

FIG. 13 is a side elevation view of a slipsheet lift mechanism; and

FIG. 14 is a bottom plan view of the slipsheet lift mechanism of FIG.13.

DETAIL DESCRIPTION OF THE PREFERRED EMBODIMENTS

The slipsheet retainer of the present invention is basically comprisedof improvements to the elevator mechanism of a depalletizer/palletizersuch as that shown in FIG. 1, and to a side plate of a sweeper mechanismof a depalletizer/palletizer such as that shown in FIG. 1. However, itshould be understood that the improvements provided by the invention maybe employed in various different types of depalletizer/palletizers, andmay also be employed in machines that perform solely the depalletizingfunction. Because the slipsheet retainer of the invention is animprovement to prior art depalletizer/palletizers, it will be describedas being applied to the machine schematically depicted in FIG. 1, itbeing understood that it could be applied to various different types ofdepalletizing/palletizing machines.

The slipsheet retainer of the present invention is basically comprisedof a platform and a sliding plate that are mounted on top of theelevator mechanism 34 of the depalletizing/palletizing machine. Theplatform is mounted on the elevator mechanism for horizontalreciprocating movement toward and away from the object infeed section Aand relative to the elevator mechanism 34. The sliding plate is mountedon top of the platform for horizontal reciprocating movement toward andaway from the object infeed section A and relative to both the platformand the elevator mechanism depending on whether it is being employed ina depalletizing or palletizing mode. In the preferred embodiment of theinvention, the horizontal reciprocating stroke of the platform is fourinches. The horizontal reciprocating stroke of the sliding surface isfour inches when employed in a depalletizing mode and six inches whenemployed in a palletizing mode.

FIG. 2 is a half-section plan view of the platform 56 of the presentinvention. In FIG. 2 the view is downward on the top of the platform andthe half-section of the platform not shown to the right of the centerline CL is a mirror image of the left-half section of the platform shownin FIG. 2 except for the presence of the pneumatic actuator 58 which isshown on the right-half section of the drawing and is not duplicated onthe left-half section of the drawing. The sliding plate 62 is shown inhalf-section in FIG. 5. The right-half section of the sliding plate tothe right of the center line CL of FIG. 5 is a mirror image of theleft-half section shown except for the presence of fastener holes forthe actuator 58 which will be explained. The sliding plate lays over thetop of the platform shown in FIG. 2 and its outside dimension isrepresented by the dashed line 62 in FIG. 2.

Referring to FIG. 2, the platform includes a pair of cross-braces 66that are secured to the top of the elevator mechanism 34. Extendinglongitudinally between the cross-braces is an angle bar 68 supportingthree rollers 72. Two additional rollers 74 are also supported by thetop cross-brace as viewed in FIG. 2. The rollers 72, 74 as well as otherrollers to be described, support the slide plate 62 for longitudinallyreciprocating movement over the platform. The actuator 58 includes acylinder connected to the brace 66 and a piston rod which extends fromthe cylinder and is connected to the underside of the slide plate 62 bya bracket 76. By selectively supplying controlled pressure to the inlets78 at the opposite ends of the actuator cylinder, the actuator extendsand retracts the bracket 76 and thereby extends and retracts the slideplate 62 through its horizontal stroke movement. By supplying pneumaticpressure to the actuator 58 to extend the bracket 76, the slide plate 62is moved through its full six inch extended stroke from the elevatorsection B toward the object infeed section A of the machine in FIG. 1and overlapping the slipsheet. In this extended position of the slideplate it is positioned for a palletizing operation where the leadingedge 82 of the slide plate is positioned over the slipsheet in thepallet load on which a layer of objects is to be added. As explainedearlier, the six inch length of stroke for palletizing is preferred,however the length of the stroke can be adjusted.

For depalletizing operation it is preferred that the slide plate 62 onlybe extended four inches longitudinally from the elevator mechanism 34toward the object infeed section A. Therefore, the six inch stroke ofthe actuator 58 must be reduced by two inches. This is accomplished by astroke limit actuator 84. The stroke limit actuator 84 is comprised of acylinder that is attached to the lower cross-brace shown in FIG. 2, thecross-brace closest to the object infeed section A. A piston rod havinga shock absorber 86 at its end extends from the cylinder 84. The pistonrod shock absorber 86 is shown in its retracted position relative to thecylinder 84. The piston rod is retracted by a spring contained in thecylinder. With the piston rod shock absorber retracted, the actuator 58may extend the slide plate 62 its full six inch stroke on extension ofthe bracket 76 from the actuator cylinder. However, when the pneumaticpressure system is controlled to provide pneumatic pressure to thestroke limit actuator 84, the piston rod shock absorber 86 is extendedtwo inches, its full length of extension. With the piston rod shockabsorber 86 extended, operation of the actuator 58 to move the slideplate 62 will cause a stop bracket 88 secured to the underside of theslide plate to contact the piston rod shock absorber 86 of the strokelimit actuator 84 resulting in the full horizontal stroke of the slideplate 62 being limited to only four inches. As explained earlier, thelimited four inch stroke of the slide plate is employed in depalletizingoperations where the leading edge 84 of the slide plate is positionedadjacent the pallet load and the slipsheet 44 adjacent to which theelevator mechanism 34 has been moved. Therefore, on extension of theactuator 58 the slide plate 62 is extended its full six inch stroke fromthe elevator section B into the object infeed section A adjacent thepallet load, and on actuation of the stroke limit actuator 84 andsubsequent actuation of the actuator 58 the slide plate 62 is extendedits four inch stroke from the elevator section B into the object infeedsection A.

FIG. 3 shows a side elevation view of the slide plate 62 resting on therollers 74 above the platform 56. The relative positions of the strokelimit actuator 84 and the piston rod shock absorber 86 to the stopbracket 88 are also shown. FIG. 9 shows the relative position of thesliding plate 62 to the platform 56 in the fully extended position ofthe sliding plate, and FIG. 10 shows the relative positions between thesliding plate 62 and the platform 56 in the retracted position of theslide plate relative to the platform. Also shown in FIGS. 3 and 4,positioning rollers 92 are provided at the corners of the slide plate62. The positioning rollers 92 engage against portions of the elevatormechanism 34 that are not shown in the drawing figures and maintain theorientation of the slide plate 62 relative to the platform 56 and theelevator mechanism 34 so that the horizontal reciprocating movement ofthe slide plate is along a straight line that is parallel to the centerline CL of the slide plate and the platform. An additional stop bracket94 is attached to the underside of the slide plate 62 and a shockabsorber 96 is mounted on the cross-brace 66 (shown at the top of FIG.2) in a position where it will engage the stop bracket 94 when the slideplate 62 is retracted by the actuator 58. The engagement of the stopbracket 94 with the shock absorber 96 absorbs shock and positivelypositions the slide plate 62 when it is retracted to its at homeposition by the actuator 58.

Pairs of trunions 98 are mounted side by side on each of thecross-braces 66. Slide rods 102, 104 extend through the pairs oftrunions 98. The pairs of slide rods 102, 104 are supported in thetrunions 98 for sliding movement of the rods. The platform 56 is securedon the innermost rods 104 so that the slide rod 104 supports theplatform for sliding reciprocating movement in the trunions 98. A pairof platform shock absorbers 106 are secured to the innermost guide rods104 in positions where the rearward most shock absorber will engage withthe rear cross-brace 66 (shown at the top of FIG. 2) to absorb shock andpositively position the platform 56 relative to the cross-brace 66 andthe elevator mechanism 34 when the platform is moved to its retractedposition, and the forward most platform shock absorber 106 will engagewith the forward cross-brace 66 when the platform 56 is moved to itsextended position to absorb shock and positively position the platformrelative to the cross-brace 66 and the elevator mechanism 34.

The platform actuator 108 controls the extension and retraction of theplatform 56 relative to the cross-braces 66 of the elevator mechanism34. The platform actuator 108 includes a cylinder having a pair ofpneumatic pressure inlets 112 and a piston rod 114 secured to therearward end of the platform 56. On selective supply of pneumaticpressure to the platform actuator 108, the piston rod 114 is extendedfrom the actuator cylinder causing the platform 56 and its slide rod 104to move relative to the trunions 98 and the cross-braces 66 to itsextended position. At its extended position the forward most platformshock absorber 106 engages against the cross-brace 66 shown at thebottom of FIG. 2 to absorb shock and limit the extension of the platformfrom the cross-brace 66 and the elevator mechanism 34 to four inches.With controlled selective supply of pneumatic pressure to the platformactuator 108 the piston rod 114 is retracted back into the actuatorcylinder causing the platform 56 and its slide rods 104 to again slidethrough the trunions 98 until the rearward platform shock absorber 106engages against the rearward elevator mechanism cross-brace 66 shown atthe top of FIG. 2 to thereby absorb shock and positively position theplatform relative to the elevator mechanism in its at home position.

A hold back bar 116 extends across the front edge of the platform 56.The hold back bar 116 is supported by the outer pair of slide rods 102in a pair of trunions 98 on the elevator mechanism cross-braces 66. Thesupport of the hold back bar 116 by the slide rod 102 in the trunions 98enables the bar and the slide rod to reciprocate horizontally relativeto the elevator mechanism cross-braces 66 and relative to the platform56. A hold back bar actuator 118 is mounted between the platform 56 andthe hold back bar 116. The actuator includes a pneumatic cylinder havinga pair of separate pneumatic pressure inputs 122 and a piston rod 124extending from the actuating cylinder to the hold back bar 116. Acontrolled selective supply of pressure to the hold back bar actuator118 extends the piston rod 124 from the actuator cylinder causing thehold back bar and its attached slide rods 102 to move relative to thetrunions 98, the elevator mechanism cross-braces 66 and the platform 56,positioning the hold back bar 116 at a spaced position forward of theplatform 56 as shown in FIG. 11. Selective control of pneumatic pressureto the hold back bar actuator 118 also causes the piston rod 124 to beretracted back into the cylinder causing the hold back bar 116 to moveback to its at home position shown in FIG. 2 and in FIG. 12. The holdback bar 116, provided just below the slide plate 62, is positioned toengage the row of objects just below the slipsheet 44 and the topmostlayer of objects 42 when the topmost layer of objects is being swept offof the slipsheet and onto the slide plate 62, thereby preventing thesliding movement of the topmost layer of objects from causing any of theobjects in the next lower layer from being knocked over. A collar 120 ismounted on the slide rod 102 and can be adjustably positioned along thelength of the slide rod to adjust the distance the hold back bar 116 canbe extended from the platform. The collar will engage against thetrunion 98 on the forward cross brace to limit the hold back barextension. Set screws secure the collar 120 to the slide rod 102. Byadjusting the position of the collar 120 on the rod, the extension ofthe hold back bar 116 can be adjusted between the distance of the fullextension of the piston rod 124 from the hold back bar actuator 118 tothe hold back bar 116 being prevented from extending from the platformby adjusting the collar 120 to a position adjacent the trunion 98 on theforward cross-brace 66.

The platform 56 also supports a plurality of rollers 132 on the top ofthe platform that in turn support the slide plate 62. The platformrollers 132 are arranged around a plurality of retainer actuators 134.The retainer actuators are best seen in FIGS. 9 and 10. Each retaineractuator 134 is comprised of a cylinder having pneumatic pressure inlets136 at its opposite ends. The rearward end of the cylinder is connectedby a pivot connection 138 to the platform 56. A piston rod 142 extendsfrom the forward end of the cylinder to a cam finger 144. A clevis orshackle 158 connects the piston rod 142 to the cam finger 144. The camfinger 144 is mounted for pivoting movement on a pivot pin 146 thatextends along the forward edge of the platform 56. Each pressure inlet136 at the opposite ends of the actuator cylinder 134 is connected by afluid conduit shown in dashed lines to a pressure manifold 152, 154. Onemanifold 152 is supplied with pressure to retract the piston rod 142into the actuator cylinder 134 and the other manifold 154 is suppliedwith pressure to extend the piston 142 from the cylinder 134. Pressureregulators are provided as part of the pneumatic pressure control system202. The pressure regulators limit the pneumatic pressure supplied bythe manifolds to the inlets 136 of the actuator 134 to a set maximumpressure. Known types of pressure regulators may be used for thispurpose. The pressure regulators isolate the two sides of the piston(not shown) in the actuator cylinder 134 from each other and isolateeach of the actuators 134 from each other so that an increase inpressure in one actuator will not influence the pressure in anotheractuator. The length of the piston rod 142 is determined so that thepiston (not shown) in the actuator cylinder 134 will never bottom out byhitting either side of the cylinder interior. The length of the pistonstroke is determined by the clevis or shackle 158 on the piston rod nearthe cam finger. When the selective pressure control extends the pistonrod 142 from the cylinder actuator 134 it quickly projects from thecylinder and its stroke movement is only stopped by the clevis 158striking the underside of the platform caused by the pivoting movementof the cam finger 144 about its pivot pin 146. The fully extendedposition of the piston rod 142 is shown in FIG. 9. To move the camfinger 144 to its lowered or retracted position shown in FIG. 9 a largepressure is supplied to the actuator 134 to quickly extend the pistonrod 142. The same high pressure value used to extend the rod from thecylinder is also used to retract the rod back into the cylinder. Theretraction of the piston into the cylinder is limited by the engagementof the clevis 158 with the front wall of the platform 56 as shown inFIG. 10. However, through experimentation, it was discovered that whenthe piston was retracted by the high pressure value and the cam fingerextended above the slide plate 62 as shown in FIG. 10, the pressure inthe actuator cylinder 134 was often too large to cause an object movingover the slipsheet 16 onto the slide plate 62 to depress the cam finger144 below the slide plate 62 in operation of the retainer, yet to beexplained. Also, where the retainer is employed in a plastic,blow-molded bottle manufacturing facility, it was observed that thehigher pressure used to raise the cam fingers would also cause damage tobottles. For a short time after a plastic bottle is blow-molded it isstill hot and its side could be indented by the cam finger where thepressure holding the fingers in their raised positions was too large.Therefore, a control 202 of the supply of pneumatic pressure to theactuator to raise the cam finger 144 was devised that would first supplythe same high pressure value used to lower the finger 144 to also raisethe finger above the slide plate 62, and then the control 202 wouldquickly decrease the pressure provided to the actuator 134 so that alesser pneumatic pressure would hold the finger 144 in its raisedposition. This lower pneumatic pressure did not present the problem ofrequiring too great a force to push the finger back down into itsretracted position nor would it cause damage to a freshly molded plasticbottle as it was swept over the finger in operation of the device.

The need for the separate pressure regulators was also discoveredthrough experimentation. It was observed that an object moving over araised finger 144 of the actuator causing the piston to move in theactuator would cause an increase in the pneumatic pressure in theactuator which would influence the pneumatic pressure in adjacentactuators. By discovering this problem through experimentation, separateregulators were provided for each actuator so that, if the pressure inone actuator is increased due to an object depressing the cam finger ofthat actuator, the increase in pressure would not affect the pressure inadjacent actuators. The top surface of the slide plate has a slightdownward taper as it extends toward its leading edge. The taperincreases the area between the top surface of the slide plate at itsleading edge and the height of the raised fingers 44 above the slideplate for catching and retaining the slipsheet.

The slide plate 62 has slots 164 along its leading edge 82 thatcorrespond to the positions of the retainer cam fingers 144. This isbest seen in FIG. 4. With the slide plate 62 in its at home positionshown in FIG. 10, the cam fingers 144 are free to be raised through theslots 164 at the end of the slide plate. When the slide plate 62 isextended relative to the platform 56 for palletizing operationsillustrated in FIG. 9, the cam fingers 144 are not raised but aremaintained in their retracted or lowered positions.

The slipsheet retainer of the invention also includes improvements madeto the sweeper mechanism side plates 26 of the prior art apparatus. Theimprovements are made to the side plate that is closest to the elevatormechanism 34. Referring to FIG. 6, the improved side plate 166 is shownviewed from the point of view of the elevator mechanism 34. The rod 168that extends across the top of the side plate 166 is the pivot rod thatconnects the side plate to the sweeper mechanism base 24 describedearlier. The improved side plate 166 itself is basically the same as theprior art side plate and operates in the same manner. The improvement isprovided by a plurality of hold down arms 168 and the arm actuators 172associated with the arms. As shown in FIG. 6 and as shown in greaterdetail in FIGS. 7 and 8, each of the actuators 172 is a pneumaticcylinder having one end connected by a pivot coupling 174 to the sideplate. A piston rod 176 projects from the opposite end of the actuatorcylinder 172 and is connected to a hold down arm 168. Each hold down arm168 is recessed in a groove 178 between rails 182 spacially arrangedside by side on the side of the side plate 166. The rails 182 are spacedapart so that the groove 178 is sufficiently large to enable theactuator arm 172 to slide up/down, forward/rearward freely through thegroove as viewed in FIGS. 7 and 8. Each of the hold down arms 168 isprovided with an oblong slot 184 and a pin 186 passes through all of therails 182 and the grooves 178 between the rails and through the oblongslots 184 of the actuator arms. Oblong openings 186 are also providedthrough the side plate 166 adjacent its bottom edge and corresponding toeach of the grooves 178. A spring bar 188 is secured across the bottomedges of the rails 182 and a plurality of leaf springs 192 project fromthe spring bar 188 and engage against the hold down arm 168. Referringto FIG. 6, pressure inlets 194 at opposite ends of the actuator cylinder172 are connected to two different pressure distribution manifolds 196,198. The pressure distribution manifolds 196, 198 are in communicationwith a source of pneumatic pressure and are selectively supplied withpneumatic pressure to extend the piston rod 176 from the actuatorcylinder 172 and retract the piston rod back in the actuator cylinder.

Pneumatic pressure supplied by the pressure control system 202 to themanifold 196 shown on the left in FIG. 6 causes the piston rods 176 ofthe arm actuators 172 to be extended from the actuators as shown in FIG.7. With the pivot connection provided by the pivot pin 185 extendingthrough the oblong slots 184 of the arms, and with the leaf spring 192exerting a biasing force on the left side of the arms as viewed in FIGS.7 and 8, as the piston rod 176 is extended from the actuator cylinder172 the arm moves downwardly and forwardly through the oblong opening186 provided in the side plate 166. When the pneumatic pressure controlsystem 202 provides pneumatic pressure to the manifold 198 and ceasesthe supply of pneumatic pressure to the manifold 196, the piston rod 176is retracted back into the actuator cylinder 172 causing the arm to moveupwardly and rearwardly. When the pivot pin 185 engages the bottom ofthe arm oblong slot 184, the arm moves back through the oblong opening186 at the bottom of the side plate to the position shown in FIG. 8.

When the supply of pneumatic pressure is removed from the manifold 198and applied to the manifold 196, this causes the hold down arms 168 tobe moved downwardly and forwardly relative to the side plate 166, thearms are positioned relative to the platform 56 and slide plate 62 asshown in FIG. 10. In this positioning of the arms, it can be seen thatthey will engage the top of the slipsheet 44 adjacent its edge closestto the elevator section B and ensure that the edge is in a positionwhere it can be engaged by the raised cam fingers 144 of the retainer.The hold down arms 168 are spacially arranged on the side plate 166 sothat as the sweeper mechanism 22 is operated to cause it to sweepobjects over the slide plate 62, the lowered arms 168 will pass betweenthe raised cam fingers 44 of the retainer and thus not interfere withtheir operation of holding back the slipsheet 44 while allowing theobjects to pass thereover.

The slipsheet retainer of the invention also includes an improvement tothe sweeper mechanism 22. It has been observed that when sweeping alayer of lighter objects, for example a layer of freshly blow-moldedplastic bottles, from a slipsheet 16, often the weight of the slipsheetleft on top of the layer of objects being swept will significantlycontribute to the friction force between the layer of objects and thelower slipsheet. The greater this friction force, the greater potentialfor an object being knocked over as it is swept off the lower slipsheet.This is especially significant in a complete pallet load of objects thatoften has a reinforcing frame constructed of wood or plastic on the topmost slipsheet that covers the top most layer of objects. To overcomethis problem, the slipsheet retainer of the invention includes a vacuummechanism added to the sweeper mechanism 22 that lifts the slipsheet ontop of the layer of objects being swept by the sweeper mechanism 22,thereby removing the weight of the slipsheet from the weight of thelayer of objects being swept and reducing the friction force between thelayer of objects being swept and the slipsheet beneath that layer ofobjects.

Referring to FIGS. 13 and 14 there is shown a vacuum mechanism 204 thatis suspended from the base 24 of the sweeper mechanism 22. To simplifythe description of the vacuum mechanism, the side plates 26 of thesweeper mechanism have been removed from the base 24 together with theiractuators, and the base 24 is shown as a rectangular framework. FIG. 13shows a side elevation view of the vacuum mechanism 204 with the leftside of the mechanism being closest to the elevator mechanism 34. FIG.14 shows a view from beneath the sweeper mechanism looking up at itsunderside.

The vacuum mechanism 204 includes a base plate 206 that has a pair ofelongated arms 208 at its opposite ends. At the opposite end of each arm208 is a downwardly depending tube 212 that has a suction cup 214 at itslower end. A pair of tubes 212 also depend downwardly from the baseplate 206 and also have suction cups 214 at their lower ends. Each ofthe tubes 212 has a vacuum hose 216 communicating therewith. The vacuumhose 216 extends from each of the tubes to a vacuum manifold 218. Avacuum pressure hose 222 extends from the vacuum manifold 218 to avacuum pressure source (not shown). The vacuum pressure source iscontrolled by the overall pneumatic pressure control system 202 toselectively supply vacuum pressure to the manifold 218 just prior tooperation of the sweeper mechanism sweeping a layer of objects eitherfrom a pallet load into the elevator section B when depalletizing, orfrom the elevator slide plate 36 onto a pallet load in the object infeedsection A when palletizing. Pairs of brackets 224 extend upwardly fromeach of the elongated arms 208. Pulleys 226 are mounted for rotation oneach of the brackets 224. Pairs of brackets 228 are mounted to oppositecross-members 232 of the sweeper mechanism base framework and pulleys234 are mounted for rotation on each of these brackets. A pair ofeyelets 236 are secured to a cross bar 238 of the sweeper mechanismframework and cables 242 are secured to each of the eyelets 236. As bestseen in FIG. 3, each of the cables extends from the eyelet 236 over apulley 234 secured to the framework 232, then under the two pulleys 226secured to one side of the elongate arms 208, and then back up over apulley 234 secured to the framework and around another pulley 244secured to the underside of the framework cross-bar 246 opposite thecross-bar 238 on which the eyelets 236 are mounted. The cables thenconnect with piston rods 248 projecting from cylinders 252 of a pair ofpneumatic actuators. The pneumatic actuators 252 are selectivelysupplied with pneumatic pressure to retract the piston rods 248 into theactuators, and are vented to cause the piston rods 248 to extend fromthe actuators. From the arrangement of the cables 242 through thepulleys 234, 226, 244, it can be seen that when the piston rod 248 isretracted into the cylinder 252 of the pneumatic actuator, the cables242 will be pulled through the pulleys causing the elongate arms 208 andbase plate 206 of the vacuum mechanism to be raised toward the frameworkof the sweeper mechanism. In reverse, venting the air pressure from theactuator cylinders 252 will cause the piston rods 248 to be extendedfrom the cylinders. The weight of the elongate arms 208 and base plate206 will then cause the arms and base plate to be lowered relative tothe framework of the sweeper mechanism.

In operation, when it is desired to lift the slipsheet off of the layerof objects to be swept, with the sweeper mechanism positioned over thelayer of objects the piston rods 248 are extended from their actuatorcylinders 252 causing the elongate arms 208 and the base plate 206 to belowered onto the slipsheet. Vacuum pressure is then supplied through thesupply hose 222 and the vacuum hoses 216 to the tubes 212 and suctioncups 214. The vacuum pressure holds the slipsheet to the suction cups214. The pressure is sufficient to hold a slipsheet having a pictureframe reinforcement. Pneumatic pressure is then supplied to the cylinderactuators 252 to retract their piston rods 248 and raise the elongatearms 208 and base plate 206 toward the framework of the sweepermechanism. With the slipsheet lifted off of the layer of objects to beswept, the weight of the layer of objects is reduced and so is itsfriction force on the slipsheet on which the layer of objects ispositioned. With the reduction in the friction force between the layerof objects and the lower slipsheet, the layer of objects is swept moreeasily off of the slipsheet and onto the slide plate 36 of the elevatormechanism. Once the layer of objects is positioned on the slide plate136, the actuator cylinders 252 are then vented causing the elongatearms 208 and base plate 206 to be lowered toward the layer of objects,and the supply of vacuum pressure is cut off from the supply hose 202causing the suction cups 214 to release the slipsheet onto the top ofthe layer of objects swept onto the slide plate.

The operation of the vacuum mechanism 204 for a palletizing mode ofoperation is substantially the same as that discussed above for thedepalletizing operation, only in reverse.

In all of the drawing figures the conduits supplying pneumatic pressureto the different actuators of the invention are shown in dashed lines inorder to simplify the drawings. The supply of pneumatic pressure iscontrolled by the pressure supply control 202 represented schematicallyin FIG. 2. The supply of pneumatic pressure to each of the individualactuators or manifolds of the apparatus is programmable and adjustableat the pneumatic supply control 202 in a similar manner to that done inprior art devices.

In operation of the slipsheet retainer of the invention in a palletizingmode on a machine such as that shown in FIG. 1, the elevator mechanism34 is first lowered until the slide plate 62 is adjacent the infeedconveyor 12 and the outfeed conveyor 38. The outfeed conveyor 38 is thenoperated in reverse to position a layer of objects in the object outfeedsection C where they await sweeping by the sweeper mechanism 22. Thesweeper mechanism 22 is then operated to surround the layer of objectsand sweep the layer of objects onto the slide plate 62. In thepalletizing mode the cam fingers 144 are retraced as shown in FIG. 9.The elevator mechanism is then operated to elevate the slide plateadjacent the slipsheet 44 placed on top of the wood pallet 18 awaitingthe objects on the infeed conveyor 12 and in the object infeed section Aor on a slipsheet on an already existing layer of objects. The pneumaticpressure supply control 202 is then operated to supply pressure to theactuator 58 that extends the slide plate 62 from the elevator mechanism34 and into the object infeed section A. The actuator 58 extends theslide plate 62 its full six inch extension so that it extends over andoverlaps the edge of the slipsheet 44 as shown in FIG. 9. With thispositioning of the slide plate, the sweeper is then again activated tosweep the objects off of the slide plate and onto the slipsheet 16 onthe pallet in the object infeed section A. The pneumatic pressure supplycontrol 202 then again operates to cause the actuator 58 to retract theslide plate 62 to its at home position over the platform 56. Theelevator mechanism 34 is then operated to move downwardly in theelevator section B in a position where it will receive the next layer ofobjects with a slipsheet thereon. The sweeper mechanism 22 sweeps thelayer of objects onto the slide plate 62 in the same manner aspreviously described. After the next layer of objects is swept onto theslide plate 62 with an additional slipsheet on this layer of objects,the elevator mechanism is then again operated to raise the layer ofobjects so that the slide plate 62 is adjacent the slipsheet on top ofthe first layer of objects swept onto the pallet in the object infeedsection A. The slide plate 62 is then extended its fully extension aswas done in the previous sequence of steps and the sweeper mechanism 22is operated to sweep the layer of objects from the slide plate onto thepreviously swept layer of objects and slipsheet in the object infeedsection A. This sequence of steps is repeated for each layer of objectsto be placed on top of the pallet 18 until the desired layers areachieved. The infeed conveyor 12 is then operated in reverse to removethe pallet load from the object infeed section A and a new pallet isplaced on the conveyor in the object infeed section with a slipsheetthereon and the loading process just described is repeated.

In the depalletizing operation of the retainer of the invention employedon the machine of FIG. 1, a pallet load is positioned on the infeedconveyor 12 and in the object infeed section A. The elevator mechanismin the object infeed section A. The elevator mechanism 34 is thenoperated to raise the elevator so that the slide plate 62 is adjacentthe topmost slipsheet 44. The pressure supply control 202 is thenoperated to extend the stroke limit actuator 84 and then extend theplatform actuator 108 and the slide plate actuator 58 together. Becausethe stroke limit actuator 84 has been extended, the slide plate actuatorcannot extend to its full six inch stroke but is limited to a four inchstroke, the same length stroke as the platform actuator 108. Therefore,both the slide plate 64 and the platform 56 move together simultaneouslyinto the object infeed section to a position adjacent the topmostslipsheet 44 and topmost layer of objects 42 to be unloaded from thepallet. At the same time the pneumatic pressure supply control providespneumatic pressure to the retainer actuators 134 causing the actuatorsto raise their cam fingers 144. Immediately after the supply of pressureis provided to the actuators 134 to raise the fingers 144, the pressureis decreased to a lesser value. The pneumatic pressure supply control202 also supplies pressure to the hold back bar actuator 118 causing thehold back bar to be extended to its position shown in FIG. 11 where itis positioned adjacent the next lower object layer 48. This positioningof the hold back bar 116 ensures that the objects in the next lowerlayer are not knocked over by the sweeping motion of the topmost layerof objects 42.

The sweeper mechanism 22 is operated as conventionally done, however,when the side plates 26 are lowered around the topmost layer of objects42, the pneumatic pressure supply control 202 is activated to supplypneumatic pressure to the hold down arm actuators 172 causing the armsto be moved to their lowered and forward positions shown in FIG. 7 andin FIG. 10. At this point in the operation of the retainer, the sweepermechanism 22 is prepared to sweep the first layer of objects 42 off theslipsheet 44 and onto the slide plate 36, the positioning of the camfingers 144 and the hold down arms 168 shown in FIG. 10 will ensure thatthe topmost slipsheet 44 will remain in place on top of the next lowerobject layer 48 as the topmost layer of objects 42 is swept by thesweeper mechanism 22 onto the slide plate 62. As the sweeper mechanismmoves across the slide plate 62, the hold down arms 68 pass between theraised cam fingers 144. When the first row of objects comes into contactwith the cam fingers 144, the movement of the objects due to thesweeping motion of the sweeper mechanism 22 will cause objects thatengage with cam fingers 144 to move those cam fingers downwardly throughtheir respective slots 164 enabling the objects to pass over the camfingers forced down and onto the slide plate 62. Those cam fingers 144that are between objects in the first row will remain in their raisedpositions and retain the slipsheet 44 from moving across the slide plate62 with the first layer of objects. Regardless of the arrangement of theobjects on the slipsheet, if there is a gap between objects at the edgeof the slipsheet as the layer of objects is swept off the slipsheet, oneor more of the cam fingers 144 will be raised into that gap and engagethe edge of the slipsheet to retain it from sliding over the slide plate62.

When the topmost layer of objects 42 has been swept onto the top of theslide plate 62, the pneumatic pressure supply control 202 is operated toretract the slide plate 62 and the platform 56 to their at homepositions on the elevator mechanism 34 while also retracting the holdback bar 116. The hold down arms 168 are also retracted to their raisedand retracted positions shown in FIG. 8. The elevator mechanism 34 andsweeper mechanism 22 are then operated in their conventional manner todeliver the swept layer of objects onto the outfeed conveyor 38 and thenreturn to the next layer of objects and the slipsheet thereon to sweepthis next layer of objects and the slipsheet thereon over the slipsheetbelow the layer of objects and onto the slide plate in the same manneras just described.

In the manner described above the slipsheet retainer of the presentinvention provides a method of retaining slipsheets under layers ofobjects swept from the slipsheets and onto elevator mechanisms in adepalletizing apparatus, where the slipsheet retainer does not interferewith the movement of a second pallet load of objects into the objectinfeed section of the depalletizing apparatus once the previous load ofobjects has been depalletized, thus providing time savings in thedepalletizing operation and a more cost efficient operation.Furthermore, the slipsheet retainer of the invention may be employed inboth depalletizing and palletizing modes, or can be modified by removingthe slide plate actuator 58 and securing the slide plate permanently tothe platform 56 where only the depalletizing function is needed.

While the present invention has been described by reference to aspecific embodiment, is should be understood that modifications andvariations of the invention may be constructed without departing fromthe scope of the invention defined in the following claims.

What is claimed:
 1. An apparatus for depalletizing objects from a palletwhere the objects are arranged in layers on the pallet with a sheetbetween adjacent layers of objects, the apparatus comprising:a bay inwhich the pallet of objects is received; a conveyor adjacent the baywhere layers of objects can be moved from the bay and received by theconveyor; a sweep supported on the bay for movement downwardly adjacenta topmost layer of objects on a pallet in the bay and movementhorizontally to move the topmost layer of objects along a path ofmovement out of the bay and onto the conveyor; a retainer between thebay and the conveyor where a sheet below the topmost layer is engaged bythe retainer and prevented from moving toward the conveyor as the sweepmoves the topmost layer of objects out of the bay and onto the conveyor,the retainer is movable between raised and lowered positions of theretainer relative to the path of movement of the topmost layer ofobjects moved by the sweep, where in the raised position the retainer isin the path of movement where it will engage the sheet and in thelowered position the retainer is out of the path of movement where itwill not engage the sheet, the retainer includes a platform having a topsliding surface and a plurality of fingers mounted on the platform formovement between raised and lowered positions of the fingers relative tothe top sliding surface, where in the raised positions of the fingersthey extend above the top sliding surface and into the path of movementof the topmost layer of objects and where in the lowered positions ofthe fingers they are retracted below the top sliding surface and out ofthe path of movement of the topmost layer of objects.
 2. The apparatusof claim 1, wherein:the top sliding surface is on a slide plate mountedon the platform and the slide plate has a plurality of slots, and thefingers are positioned on the platform to pass through the slots as theyare moved between their raised and lower positions.
 3. The apparatus ofclaim 2, wherein:the slide plate is mounted on the platform for movementof the slide plate between extended and retracted positions of the slideplate relative to the platform, where in the extended position of theslide plate the slide plate extends over a pallet received in the bayand in the retracted position of the slide plate the slide plate doesnot extend over a pallet received by the bay.
 4. The apparatus of claim2, wherein:the slide plate is mounted on the platform for movement ofthe slide plate between extended and retracted positions of the slideplate relative to the platform where in the extended position of theslide plate the plurality of slots are spaced from the plurality offingers and in the retracted position of the slide plate the pluralityof slots are positioned above the plurality of fingers.
 5. The apparatusof claim 2, wherein:the platform is mounted on a base adjacent the bayfor movement of the platform relative to the base and the bay between anextended position of the platform where the fingers are positioned inthe bay and a retracted position of the platform where the fingers areoutside the bay.
 6. The apparatus of claim 5, wherein:the slide plate ismounted on the platform for movement of the slide plate between extendedand retracted positions of the slide plate relative to the platformwhere in the extended position of the slide plate the plurality of slotsare spaced from the plurality of fingers and in the retracted positionof the slide plate the plurality of slots are positioned above theplurality of fingers.
 7. The apparatus of claim 1, wherein:the retainerincludes a plurality of pneumatic actuators and each pneumatic actuatorof the plurality of pneumatic actuators moves one of the plurality offingers between its raised and lowered positions.
 8. The apparatus ofclaim 7, wherein:each pneumatic actuator has a pressure regulator thatlimits air pressure in the pneumatic actuator to a maximum level.
 9. Theapparatus of claim 7, wherein:a pressure control supplies air above aset pressure to the plurality of pneumatic actuators to cause thepneumatic actuators to raise the plurality of fingers and the pressurecontrol supplies air below the set pressure to the plurality ofpneumatic actuators after the pneumatic actuators have raised thefingers to maintain the fingers in their raised positions.
 10. Anapparatus for depalletizing objects from a pallet where the objects arearranged in layers on the pallet with a sheet between adjacent layers ofobjects, the apparatus comprising:a bay in which the pallet of objectsis received; a conveyor adjacent the bay where layers of objects can bemoved from the bay and received by the conveyor; a sweep supported onthe bay for movement downwardly adjacent a topmost layer of objects on apallet in the bay and movement horizontally to move the topmost layer ofobjects along a path of movement out of the bay and onto the conveyor; aretainer between the bay and the conveyor where a sheet below thetopmost layer is engaged by the retainer and prevented from movingtoward the conveyor as the sweep moves the topmost layer of objects outof the bay and onto the conveyor; and a hold back bar is positionedbelow the retainer where it will engage objects in a layer of objectsbelow the topmost layer of objects as the sweep moves the topmost layerof objects out of the bay and onto the conveyor.
 11. An apparatus fordepalletizing objects from a pallet where the objects are arranged inlayers on the pallet with a sheet between adjacent layers of objects,the apparatus comprising:a bay in which the pallet of objects isreceived; a conveyor adjacent the bay where layers of objects can bemoved from the bay and received by the conveyor; a sweep supported onthe bay for movement downwardly adjacent a topmost layer of objects on apallet in the bay and movement horizontally to move the topmost layer ofobjects along a path of movement out of the bay and onto the conveyor; aretainer between the bay and the conveyor where a sheet below thetopmost layer is engaged by the retainer and prevented from movingtoward the conveyor as the sweep moves the topmost layer of objects outof the bay and onto the conveyor, the retainer is movable between raisedand lowered positions of the retainer relative to the path of movementof the topmost layer of objects moved by the sweep, where in the raisedposition the retainer is in the path of movement where it will engagethe sheet and in the lowered position the retainer is out of the path ofmovement where it will not engage the sheet; and a pneumatic actuatormoves the retainer between its raised and lowered positions and apressure control supplies air above a set pressure to move the retainerfrom its lowered position to its raised position and the pressurecontrol supplies air below the set pressure to the retainer after theretainer has been moved to the raised position.
 12. The apparatus ofclaim 11, wherein:an elevator is supported on the bay for upward anddownward movement relative to the bay and conveyor to position thetopmost layer of objects on the pallet in the bay adjacent the conveyor.13. The apparatus of claim 11, wherein:the sweep has a plurality of armsmounted on the sweep for movement between raised and lowered positionsof the arms relative to the sweep, and the arms are positioned on thesweep so that when the sweep is moved adjacent the topmost layer ofobjects on a pallet in the bay, when the arms are moved to their loweredpositions the arms are positioned over the sheet under the topmost layerof objects, and when the arms are moved to their raised positions thearms are positioned to a side of the sheet under the topmost layer ofobjects.
 14. The apparatus of claim 11, wherein:the sweep has a vacuummechanism attached thereto that is selectively actuated to raise aslipsheet off of the topmost layer of objects.
 15. An apparatus fordepalletizing objects from a pallet where the objects are arranged inlayers on the pallet with a sheet between adjacent layers of objects,the apparatus comprising:a bay in which the pallet of objects isreceived; a platform having a top sliding surface adjacent the bay; asweep supported on the bay for movement adjacent a topmost layer ofobjects on a pallet in the bay and movement horizontally to move thetopmost layer of objects along a path of movement across the sheet belowthe topmost layer of objects out of the bay and onto the platform topsliding surface; a retainer between the bay and the platform, theretainer being movable between raised and lowered positions relative tothe path of movement of the topmost layer of objects moved by the sweep,where in the raised position the retainer is in the path of movementwhere it will engage the sheet under the topmost layer of objects as thetopmost layer of objects is swept across the sheet out of the bay andonto the platform top sliding surface, the retainer includes at leastone pneumatic actuator that is operable to raise and lower the retainer,and a pressure control that supplies pressure above a set pressure tothe pneumatic actuator to move the retainer from its lowered position toits raised position and supplies pressure below the set pressure to thepneumatic actuator to hold the retainer in its raised position.
 16. Anapparatus for depalletizing objects from a pallet where the objects arearranged in layers on the pallet with a sheet between adjacent layers ofobjects, the apparatus comprising:a bay in which the pallet of objectsis received; a platform having a top sliding surface adjacent the bay; asweep supported on the bay for movement adjacent a topmost layer ofobjects on a pallet in the bay and movement horizontally to move thetopmost layer of objects along a path of movement across the sheet belowthe topmost layer of objects out of the bay and onto the platform topsliding surface; a retainer between the bay and the platform, theretainer being movable between raised and lowered positions relative tothe path of movement of the topmost layer of objects moved by the sweep,where in the raised position the retainer is in the path of movementwhere it will engage the sheet under the topmost layer of objects as thetopmost layer of objects is swept across the sheet out of the bay andonto the platform top sliding surface, the retainer includes a pluralityof fingers mounted on the platform for movement of the fingers betweenraised and lowered positions relative to the platform where in theraised positions of the fingers they extend above the platform topsliding surface and into the path of movement of the topmost layer ofobjects and where in the lowered positions of the fingers they areretracted below the platform top sliding surface and out of the path ofmovement of the topmost layer of objects.
 17. The apparatus of claim 16,wherein:the retainer includes a plurality of pneumatic actuators andeach pneumatic actuator of the plurality of pneumatic actuators movesone of the plurality of fingers between its raised and lowered positionsand each pneumatic actuator has a pressure regulator that limits airpressure in the pneumatic actuator to a maximum level.
 18. The actuatorof claim 16, wherein:the retainer includes a plurality of pneumaticactuators and each pneumatic actuator of the plurality of pneumaticactuators moves one of the plurality of fingers between its raised andlowered positions, and a pressure control that supplies air above a setpressure to the plurality of pneumatic actuators to raise the pluralityof fingers and supplies air below the set pressure to the plurality ofactuators to hold the plurality of fingers in their raised positions.19. The apparatus of claim 15, wherein:the sweep has a vacuum mechanismattached thereto that is selectively actuated to raise a slipsheet offof the topmost layer of objects.